Start moving to provide an improving contrast (6)

I believe the answer is:

setoff

I'm a little stuck... Click here to teach me more about this clue!

'start' is the definition.
(thesaurus)

'moving to provide an improving contrast' is the wordplay.
I cannot quite understand how this works, but
'to' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for setoff that I've seen is " Display - mount - start journey".)

I've seen this clue in The Irish Independent.

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